/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.hc.client5.http.impl.async;

import java.io.Closeable;
import java.io.IOException;
import java.net.ProxySelector;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.ThreadFactory;

import org.apache.hc.client5.http.ConnectionKeepAliveStrategy;
import org.apache.hc.client5.http.SchemePortResolver;
import org.apache.hc.client5.http.SystemDefaultDnsResolver;
import org.apache.hc.client5.http.async.AsyncExecChainHandler;
import org.apache.hc.client5.http.auth.AuthSchemeProvider;
import org.apache.hc.client5.http.auth.CredentialsProvider;
import org.apache.hc.client5.http.config.AuthSchemes;
import org.apache.hc.client5.http.config.RequestConfig;
import org.apache.hc.client5.http.cookie.BasicCookieStore;
import org.apache.hc.client5.http.cookie.CookieSpecProvider;
import org.apache.hc.client5.http.cookie.CookieStore;
import org.apache.hc.client5.http.impl.DefaultConnectionKeepAliveStrategy;
import org.apache.hc.client5.http.impl.DefaultSchemePortResolver;
import org.apache.hc.client5.http.impl.DefaultUserTokenHandler;
import org.apache.hc.client5.http.impl.IdleConnectionEvictor;
import org.apache.hc.client5.http.impl.NamedElementChain;
import org.apache.hc.client5.http.impl.NoopUserTokenHandler;
import org.apache.hc.client5.http.impl.auth.BasicSchemeFactory;
import org.apache.hc.client5.http.impl.auth.CredSspSchemeFactory;
import org.apache.hc.client5.http.impl.auth.DigestSchemeFactory;
import org.apache.hc.client5.http.impl.auth.KerberosSchemeFactory;
import org.apache.hc.client5.http.impl.auth.NTLMSchemeFactory;
import org.apache.hc.client5.http.impl.auth.SPNegoSchemeFactory;
import org.apache.hc.client5.http.impl.auth.SystemDefaultCredentialsProvider;
import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManagerBuilder;
import org.apache.hc.client5.http.impl.protocol.DefaultAuthenticationStrategy;
import org.apache.hc.client5.http.impl.protocol.DefaultRedirectStrategy;
import org.apache.hc.client5.http.impl.routing.DefaultProxyRoutePlanner;
import org.apache.hc.client5.http.impl.routing.DefaultRoutePlanner;
import org.apache.hc.client5.http.impl.routing.SystemDefaultRoutePlanner;
import org.apache.hc.client5.http.impl.sync.BasicCredentialsProvider;
import org.apache.hc.client5.http.impl.sync.ChainElements;
import org.apache.hc.client5.http.impl.sync.CookieSpecRegistries;
import org.apache.hc.client5.http.impl.sync.DefaultHttpRequestRetryHandler;
import org.apache.hc.client5.http.nio.AsyncClientConnectionManager;
import org.apache.hc.client5.http.protocol.AuthenticationStrategy;
import org.apache.hc.client5.http.protocol.RedirectStrategy;
import org.apache.hc.client5.http.protocol.RequestAddCookies;
import org.apache.hc.client5.http.protocol.RequestAuthCache;
import org.apache.hc.client5.http.protocol.RequestDefaultHeaders;
import org.apache.hc.client5.http.protocol.RequestExpectContinue;
import org.apache.hc.client5.http.protocol.ResponseProcessCookies;
import org.apache.hc.client5.http.protocol.UserTokenHandler;
import org.apache.hc.client5.http.routing.HttpRoutePlanner;
import org.apache.hc.client5.http.sync.HttpRequestRetryHandler;
import org.apache.hc.core5.annotation.Internal;
import org.apache.hc.core5.concurrent.DefaultThreadFactory;
import org.apache.hc.core5.function.Callback;
import org.apache.hc.core5.http.ConnectionReuseStrategy;
import org.apache.hc.core5.http.Header;
import org.apache.hc.core5.http.HttpException;
import org.apache.hc.core5.http.HttpHost;
import org.apache.hc.core5.http.HttpRequest;
import org.apache.hc.core5.http.HttpRequestInterceptor;
import org.apache.hc.core5.http.HttpResponse;
import org.apache.hc.core5.http.HttpResponseInterceptor;
import org.apache.hc.core5.http.config.CharCodingConfig;
import org.apache.hc.core5.http.config.H1Config;
import org.apache.hc.core5.http.config.Lookup;
import org.apache.hc.core5.http.config.RegistryBuilder;
import org.apache.hc.core5.http.impl.DefaultConnectionReuseStrategy;
import org.apache.hc.core5.http.nio.AsyncPushConsumer;
import org.apache.hc.core5.http.nio.HandlerFactory;
import org.apache.hc.core5.http.nio.command.ShutdownCommand;
import org.apache.hc.core5.http.protocol.DefaultHttpProcessor;
import org.apache.hc.core5.http.protocol.HttpContext;
import org.apache.hc.core5.http.protocol.HttpProcessor;
import org.apache.hc.core5.http.protocol.HttpProcessorBuilder;
import org.apache.hc.core5.http.protocol.RequestTargetHost;
import org.apache.hc.core5.http.protocol.RequestUserAgent;
import org.apache.hc.core5.http2.HttpVersionPolicy;
import org.apache.hc.core5.http2.config.H2Config;
import org.apache.hc.core5.http2.protocol.H2RequestConnControl;
import org.apache.hc.core5.http2.protocol.H2RequestContent;
import org.apache.hc.core5.http2.protocol.H2RequestTargetHost;
import org.apache.hc.core5.io.ShutdownType;
import org.apache.hc.core5.pool.ConnPoolControl;
import org.apache.hc.core5.reactor.DefaultConnectingIOReactor;
import org.apache.hc.core5.reactor.IOEventHandlerFactory;
import org.apache.hc.core5.reactor.IOReactorConfig;
import org.apache.hc.core5.reactor.IOReactorException;
import org.apache.hc.core5.reactor.IOSession;
import org.apache.hc.core5.util.Args;
import org.apache.hc.core5.util.TimeValue;
import org.apache.hc.core5.util.VersionInfo;

/**
 * Builder for {@link CloseableHttpAsyncClient} instances.
 * <p>
 * When a particular component is not explicitly set this class will
 * use its default implementation. System properties will be taken
 * into account when configuring the default implementations when
 * {@link #useSystemProperties()} method is called prior to calling
 * {@link #build()}.
 * </p>
 * <ul>
 *  <li>http.proxyHost</li>
 *  <li>http.proxyPort</li>
 *  <li>http.nonProxyHosts</li>
 *  <li>http.keepAlive</li>
 *  <li>http.agent</li>
 * </ul>
 * <p>
 * Please note that some settings used by this class can be mutually
 * exclusive and may not apply when building {@link CloseableHttpAsyncClient}
 * instances.
 * </p>
 *
 * @since 5.0
 */
public class HttpAsyncClientBuilder {

    private static class RequestInterceptorEntry {

        enum Postion { FIRST, LAST }

        final RequestInterceptorEntry.Postion postion;
        final HttpRequestInterceptor interceptor;

        private RequestInterceptorEntry(final RequestInterceptorEntry.Postion postion, final HttpRequestInterceptor interceptor) {
            this.postion = postion;
            this.interceptor = interceptor;
        }
    }

    private static class ResponseInterceptorEntry {

        enum Postion { FIRST, LAST }

        final ResponseInterceptorEntry.Postion postion;
        final HttpResponseInterceptor interceptor;

        private ResponseInterceptorEntry(final ResponseInterceptorEntry.Postion postion, final HttpResponseInterceptor interceptor) {
            this.postion = postion;
            this.interceptor = interceptor;
        }
    }

    private static class ExecInterceptorEntry {

        enum Postion { BEFORE, AFTER, REPLACE }

        final ExecInterceptorEntry.Postion postion;
        final String name;
        final AsyncExecChainHandler interceptor;
        final String existing;

        private ExecInterceptorEntry(
                final ExecInterceptorEntry.Postion postion,
                final String name,
                final AsyncExecChainHandler interceptor,
                final String existing) {
            this.postion = postion;
            this.name = name;
            this.interceptor = interceptor;
            this.existing = existing;
        }

    }

    private HttpVersionPolicy versionPolicy;
    private AsyncClientConnectionManager connManager;
    private boolean connManagerShared;
    private IOReactorConfig ioReactorConfig;
    private H1Config h1Config;
    private H2Config h2Config;
    private CharCodingConfig charCodingConfig;
    private SchemePortResolver schemePortResolver;
    private ConnectionKeepAliveStrategy keepAliveStrategy;
    private UserTokenHandler userTokenHandler;
    private AuthenticationStrategy targetAuthStrategy;
    private AuthenticationStrategy proxyAuthStrategy;

    private LinkedList<RequestInterceptorEntry> requestInterceptors;
    private LinkedList<ResponseInterceptorEntry> responseInterceptors;
    private LinkedList<ExecInterceptorEntry> execInterceptors;

    private HttpRoutePlanner routePlanner;
    private RedirectStrategy redirectStrategy;
    private HttpRequestRetryHandler retryHandler;

    private ConnectionReuseStrategy reuseStrategy;

    private Lookup<AuthSchemeProvider> authSchemeRegistry;
    private Lookup<CookieSpecProvider> cookieSpecRegistry;
    private CookieStore cookieStore;
    private CredentialsProvider credentialsProvider;

    private String userAgent;
    private HttpHost proxy;
    private Collection<? extends Header> defaultHeaders;
    private RequestConfig defaultRequestConfig;
    private boolean evictExpiredConnections;
    private boolean evictIdleConnections;
    private TimeValue maxIdleTime;

    private boolean systemProperties;
    private boolean automaticRetriesDisabled;
    private boolean redirectHandlingDisabled;
    private boolean cookieManagementDisabled;
    private boolean authCachingDisabled;
    private boolean connectionStateDisabled;

    private ThreadFactory threadFactory;

    private List<Closeable> closeables;

    public static HttpAsyncClientBuilder create() {
        return new HttpAsyncClientBuilder();
    }

    protected HttpAsyncClientBuilder() {
        super();
    }

    /**
     * Sets HTTP protocol version policy.
     */
    public final HttpAsyncClientBuilder setVersionPolicy(final HttpVersionPolicy versionPolicy) {
        this.versionPolicy = versionPolicy;
        return this;
    }

    /**
     * Sets {@link H1Config} configuration.
     */
    public final HttpAsyncClientBuilder setH1Config(final H1Config h1Config) {
        this.h1Config = h1Config;
        return this;
    }

    /**
     * Sets {@link H2Config} configuration.
     */
    public final HttpAsyncClientBuilder setH2Config(final H2Config h2Config) {
        this.h2Config = h2Config;
        return this;
    }

    /**
     * Assigns {@link AsyncClientConnectionManager} instance.
     */
    public final HttpAsyncClientBuilder setConnectionManager(final AsyncClientConnectionManager connManager) {
        this.connManager = connManager;
        return this;
    }

    /**
     * Defines the connection manager is to be shared by multiple
     * client instances.
     * <p>
     * If the connection manager is shared its life-cycle is expected
     * to be managed by the caller and it will not be shut down
     * if the client is closed.
     *
     * @param shared defines whether or not the connection manager can be shared
     *  by multiple clients.
     */
    public final HttpAsyncClientBuilder setConnectionManagerShared(final boolean shared) {
        this.connManagerShared = shared;
        return this;
    }

    /**
     * Sets {@link IOReactorConfig} configuration.
     */
    public final HttpAsyncClientBuilder setIOReactorConfig(final IOReactorConfig ioReactorConfig) {
        this.ioReactorConfig = ioReactorConfig;
        return this;
    }

    /**
     * Sets {@link CharCodingConfig} configuration.
     */
    public final HttpAsyncClientBuilder setCharCodingConfig(final CharCodingConfig charCodingConfig) {
        this.charCodingConfig = charCodingConfig;
        return this;
    }

    /**
     * Assigns {@link ConnectionReuseStrategy} instance.
     * <p>
     * Please note this strategy applies to HTTP/1.0 and HTTP/1.1 connections only
     */
    public final HttpAsyncClientBuilder setConnectionReuseStrategy(final ConnectionReuseStrategy reuseStrategy) {
        this.reuseStrategy = reuseStrategy;
        return this;
    }

    /**
     * Assigns {@link ConnectionKeepAliveStrategy} instance.
     */
    public final HttpAsyncClientBuilder setKeepAliveStrategy(final ConnectionKeepAliveStrategy keepAliveStrategy) {
        this.keepAliveStrategy = keepAliveStrategy;
        return this;
    }

    /**
     * Assigns {@link UserTokenHandler} instance.
     * <p>
     * Please note this value can be overridden by the {@link #disableConnectionState()}
     * method.
     * </p>
     */
    public final HttpAsyncClientBuilder setUserTokenHandler(final UserTokenHandler userTokenHandler) {
        this.userTokenHandler = userTokenHandler;
        return this;
    }

    /**
     * Assigns {@link AuthenticationStrategy} instance for target
     * host authentication.
     */
    public final HttpAsyncClientBuilder setTargetAuthenticationStrategy(
            final AuthenticationStrategy targetAuthStrategy) {
        this.targetAuthStrategy = targetAuthStrategy;
        return this;
    }

    /**
     * Assigns {@link AuthenticationStrategy} instance for proxy
     * authentication.
     */
    public final HttpAsyncClientBuilder setProxyAuthenticationStrategy(
            final AuthenticationStrategy proxyAuthStrategy) {
        this.proxyAuthStrategy = proxyAuthStrategy;
        return this;
    }

    /**
     * Adds this protocol interceptor to the head of the protocol processing list.
     */
    public final HttpAsyncClientBuilder addRequestInterceptorFirst(final HttpResponseInterceptor interceptor) {
        Args.notNull(interceptor, "Interceptor");
        if (responseInterceptors == null) {
            responseInterceptors = new LinkedList<>();
        }
        responseInterceptors.add(new ResponseInterceptorEntry(ResponseInterceptorEntry.Postion.FIRST, interceptor));
        return this;
    }

    /**
     * Adds this protocol interceptor to the tail of the protocol processing list.
     */
    public final HttpAsyncClientBuilder addResponseInterceptorLast(final HttpResponseInterceptor interceptor) {
        Args.notNull(interceptor, "Interceptor");
        if (responseInterceptors == null) {
            responseInterceptors = new LinkedList<>();
        }
        responseInterceptors.add(new ResponseInterceptorEntry(ResponseInterceptorEntry.Postion.LAST, interceptor));
        return this;
    }

    /**
     * Adds this execution interceptor before an existing interceptor.
     */
    public final HttpAsyncClientBuilder addExecInterceptorBefore(final String existing, final String name, final AsyncExecChainHandler interceptor) {
        Args.notBlank(existing, "Existing");
        Args.notBlank(name, "Name");
        Args.notNull(interceptor, "Interceptor");
        if (execInterceptors == null) {
            execInterceptors = new LinkedList<>();
        }
        execInterceptors.add(new ExecInterceptorEntry(ExecInterceptorEntry.Postion.BEFORE, name, interceptor, existing));
        return this;
    }

    /**
     * Adds this execution interceptor after interceptor with the given name.
     */
    public final HttpAsyncClientBuilder addExecInterceptorAfter(final String existing, final String name, final AsyncExecChainHandler interceptor) {
        Args.notBlank(existing, "Existing");
        Args.notBlank(name, "Name");
        Args.notNull(interceptor, "Interceptor");
        if (execInterceptors == null) {
            execInterceptors = new LinkedList<>();
        }
        execInterceptors.add(new ExecInterceptorEntry(ExecInterceptorEntry.Postion.AFTER, name, interceptor, existing));
        return this;
    }

    /**
     * Replace an existing interceptor with the given name with new interceptor.
     */
    public final HttpAsyncClientBuilder replaceExecInterceptor(final String existing, final AsyncExecChainHandler interceptor) {
        Args.notBlank(existing, "Existing");
        Args.notNull(interceptor, "Interceptor");
        if (execInterceptors == null) {
            execInterceptors = new LinkedList<>();
        }
        execInterceptors.add(new ExecInterceptorEntry(ExecInterceptorEntry.Postion.REPLACE, existing, interceptor, existing));
        return this;
    }

    /**
     * Adds this protocol interceptor to the head of the protocol processing list.
     */
    public final HttpAsyncClientBuilder addRequestInterceptorFirst(final HttpRequestInterceptor interceptor) {
        Args.notNull(interceptor, "Interceptor");
        if (requestInterceptors == null) {
            requestInterceptors = new LinkedList<>();
        }
        requestInterceptors.add(new RequestInterceptorEntry(RequestInterceptorEntry.Postion.FIRST, interceptor));
        return this;
    }

    /**
     * Adds this protocol interceptor to the tail of the protocol processing list.
     */
    public final HttpAsyncClientBuilder addResponseInterceptorLast(final HttpRequestInterceptor interceptor) {
        Args.notNull(interceptor, "Interceptor");
        if (requestInterceptors == null) {
            requestInterceptors = new LinkedList<>();
        }
        requestInterceptors.add(new RequestInterceptorEntry(RequestInterceptorEntry.Postion.LAST, interceptor));
        return this;
    }

    /**
     * Assigns {@link HttpRequestRetryHandler} instance.
     * <p>
     * Please note this value can be overridden by the {@link #disableAutomaticRetries()}
     * method.
     */
    public final HttpAsyncClientBuilder setRetryHandler(final HttpRequestRetryHandler retryHandler) {
        this.retryHandler = retryHandler;
        return this;
    }

    /**
     * Assigns {@link RedirectStrategy} instance.
     * <p>
     * Please note this value can be overridden by the {@link #disableRedirectHandling()}
     * method.
     * </p>
     */
    public HttpAsyncClientBuilder setRedirectStrategy(final RedirectStrategy redirectStrategy) {
        this.redirectStrategy = redirectStrategy;
        return this;
    }

    /**
     * Assigns {@link SchemePortResolver} instance.
     */
    public final HttpAsyncClientBuilder setSchemePortResolver(final SchemePortResolver schemePortResolver) {
        this.schemePortResolver = schemePortResolver;
        return this;
    }

    /**
     * Assigns {@link ThreadFactory} instance.
     */
    public final HttpAsyncClientBuilder setThreadFactory(final ThreadFactory threadFactory) {
        this.threadFactory = threadFactory;
        return this;
    }

    /**
     * Assigns {@code User-Agent} value.
     */
    public final HttpAsyncClientBuilder setUserAgent(final String userAgent) {
        this.userAgent = userAgent;
        return this;
    }

    /**
     * Assigns default request header values.
     */
    public final HttpAsyncClientBuilder setDefaultHeaders(final Collection<? extends Header> defaultHeaders) {
        this.defaultHeaders = defaultHeaders;
        return this;
    }

    /**
     * Assigns default proxy value.
     * <p>
     * Please note this value can be overridden by the {@link #setRoutePlanner(
     *   HttpRoutePlanner)} method.
     */
    public final HttpAsyncClientBuilder setProxy(final HttpHost proxy) {
        this.proxy = proxy;
        return this;
    }

    /**
     * Assigns {@link HttpRoutePlanner} instance.
     */
    public final HttpAsyncClientBuilder setRoutePlanner(final HttpRoutePlanner routePlanner) {
        this.routePlanner = routePlanner;
        return this;
    }

    /**
     * Assigns default {@link CredentialsProvider} instance which will be used
     * for request execution if not explicitly set in the client execution
     * context.
     */
    public final HttpAsyncClientBuilder setDefaultCredentialsProvider(final CredentialsProvider credentialsProvider) {
        this.credentialsProvider = credentialsProvider;
        return this;
    }

    /**
     * Assigns default {@link org.apache.hc.client5.http.auth.AuthScheme} registry which will
     * be used for request execution if not explicitly set in the client execution
     * context.
     */
    public final HttpAsyncClientBuilder setDefaultAuthSchemeRegistry(final Lookup<AuthSchemeProvider> authSchemeRegistry) {
        this.authSchemeRegistry = authSchemeRegistry;
        return this;
    }

    /**
     * Assigns default {@link org.apache.hc.client5.http.cookie.CookieSpec} registry
     * which will be used for request execution if not explicitly set in the client
     * execution context.
     */
    public final HttpAsyncClientBuilder setDefaultCookieSpecRegistry(final Lookup<CookieSpecProvider> cookieSpecRegistry) {
        this.cookieSpecRegistry = cookieSpecRegistry;
        return this;
    }

    /**
     * Assigns default {@link CookieStore} instance which will be used for
     * request execution if not explicitly set in the client execution context.
     */
    public final HttpAsyncClientBuilder setDefaultCookieStore(final CookieStore cookieStore) {
        this.cookieStore = cookieStore;
        return this;
    }

    /**
     * Assigns default {@link RequestConfig} instance which will be used
     * for request execution if not explicitly set in the client execution
     * context.
     */
    public final HttpAsyncClientBuilder setDefaultRequestConfig(final RequestConfig config) {
        this.defaultRequestConfig = config;
        return this;
    }

    /**
     * Use system properties when creating and configuring default
     * implementations.
     */
    public final HttpAsyncClientBuilder useSystemProperties() {
        this.systemProperties = true;
        return this;
    }

    /**
     * Disables connection state tracking.
     */
    public final HttpAsyncClientBuilder disableConnectionState() {
        connectionStateDisabled = true;
        return this;
    }

    /**
     * Disables automatic redirect handling.
     */
    public final HttpAsyncClientBuilder disableRedirectHandling() {
        redirectHandlingDisabled = true;
        return this;
    }

    /**
     * Disables automatic request recovery and re-execution.
     */
    public final HttpAsyncClientBuilder disableAutomaticRetries() {
        automaticRetriesDisabled = true;
        return this;
    }

    /**
     * Disables state (cookie) management.
     */
    public final HttpAsyncClientBuilder disableCookieManagement() {
        this.cookieManagementDisabled = true;
        return this;
    }

    /**
     * Disables authentication scheme caching.
     */
    public final HttpAsyncClientBuilder disableAuthCaching() {
        this.authCachingDisabled = true;
        return this;
    }

    /**
     * Makes this instance of HttpClient proactively evict expired connections from the
     * connection pool using a background thread.
     * <p>
     * One MUST explicitly close HttpClient with {@link CloseableHttpAsyncClient#close()} in order
     * to stop and release the background thread.
     * <p>
     * Please note this method has no effect if the instance of HttpClient is configuted to
     * use a shared connection manager.
     *
     * @see #setConnectionManagerShared(boolean)
     * @see ConnPoolControl#closeExpired()
     */
    public final HttpAsyncClientBuilder evictExpiredConnections() {
        evictExpiredConnections = true;
        return this;
    }

    /**
     * Makes this instance of HttpClient proactively evict idle connections from the
     * connection pool using a background thread.
     * <p>
     * One MUST explicitly close HttpClient with {@link CloseableHttpAsyncClient#close()}
     * in order to stop and release the background thread.
     * <p>
     * Please note this method has no effect if the instance of HttpClient is configuted to
     * use a shared connection manager.
     *
     * @see #setConnectionManagerShared(boolean)
     * @see ConnPoolControl#closeIdle(TimeValue)
     *
     * @param maxIdleTime maximum time persistent connections can stay idle while kept alive
     * in the connection pool. Connections whose inactivity period exceeds this value will
     * get closed and evicted from the pool.
     */
    public final HttpAsyncClientBuilder evictIdleConnections(final TimeValue maxIdleTime) {
        this.evictIdleConnections = true;
        this.maxIdleTime = maxIdleTime;
        return this;
    }

    /**
     * Request exec chain customization and extension.
     * <p>
     * For internal use.
     */
    @Internal
    protected void customizeExecChain(final NamedElementChain<AsyncExecChainHandler> execChainDefinition) {
    }

    /**
     * Adds to the list of {@link Closeable} resources to be managed by the client.
     * <p>
     * For internal use.
     */
    @Internal
    protected void addCloseable(final Closeable closeable) {
        if (closeable == null) {
            return;
        }
        if (closeables == null) {
            closeables = new ArrayList<>();
        }
        closeables.add(closeable);
    }

    public CloseableHttpAsyncClient build() {
        AsyncClientConnectionManager connManagerCopy = this.connManager;
        if (connManagerCopy == null) {
            connManagerCopy = PoolingAsyncClientConnectionManagerBuilder.create().build();
        }

        ConnectionKeepAliveStrategy keepAliveStrategyCopy = this.keepAliveStrategy;
        if (keepAliveStrategyCopy == null) {
            keepAliveStrategyCopy = DefaultConnectionKeepAliveStrategy.INSTANCE;
        }

        UserTokenHandler userTokenHandlerCopy = this.userTokenHandler;
        if (userTokenHandlerCopy == null) {
            if (!connectionStateDisabled) {
                userTokenHandlerCopy = DefaultUserTokenHandler.INSTANCE;
            } else {
                userTokenHandlerCopy = NoopUserTokenHandler.INSTANCE;
            }
        }

        final NamedElementChain<AsyncExecChainHandler> execChainDefinition = new NamedElementChain<>();
        execChainDefinition.addLast(
                new AsyncMainClientExec(keepAliveStrategyCopy, userTokenHandlerCopy),
                ChainElements.MAIN_TRANSPORT.name());

        AuthenticationStrategy targetAuthStrategyCopy = this.targetAuthStrategy;
        if (targetAuthStrategyCopy == null) {
            targetAuthStrategyCopy = DefaultAuthenticationStrategy.INSTANCE;
        }
        AuthenticationStrategy proxyAuthStrategyCopy = this.proxyAuthStrategy;
        if (proxyAuthStrategyCopy == null) {
            proxyAuthStrategyCopy = DefaultAuthenticationStrategy.INSTANCE;
        }

        String userAgentCopy = this.userAgent;
        if (userAgentCopy == null) {
            if (systemProperties) {
                userAgentCopy = System.getProperty("http.agent");
            }
            if (userAgentCopy == null) {
                userAgentCopy = VersionInfo.getSoftwareInfo("Apache-HttpAsyncClient",
                        "org.apache.hc.client5", getClass());
            }
        }

        execChainDefinition.addFirst(
                new AsyncConnectExec(
                        new DefaultHttpProcessor(new RequestTargetHost(), new RequestUserAgent(userAgentCopy)),
                        proxyAuthStrategyCopy),
                ChainElements.CONNECT.name());

        final HttpProcessorBuilder b = HttpProcessorBuilder.create();
        if (requestInterceptors != null) {
            for (final RequestInterceptorEntry entry: requestInterceptors) {
                if (entry.postion == RequestInterceptorEntry.Postion.FIRST) {
                    b.addFirst(entry.interceptor);
                }
            }
        }
        if (responseInterceptors != null) {
            for (final ResponseInterceptorEntry entry: responseInterceptors) {
                if (entry.postion == ResponseInterceptorEntry.Postion.FIRST) {
                    b.addFirst(entry.interceptor);
                }
            }
        }
        b.addAll(
                new RequestDefaultHeaders(defaultHeaders),
                new RequestUserAgent(userAgentCopy),
                new RequestExpectContinue());
        if (!cookieManagementDisabled) {
            b.add(new RequestAddCookies());
        }
        if (!authCachingDisabled) {
            b.add(new RequestAuthCache());
        }
        if (!cookieManagementDisabled) {
            b.add(new ResponseProcessCookies());
        }
        if (requestInterceptors != null) {
            for (final RequestInterceptorEntry entry: requestInterceptors) {
                if (entry.postion == RequestInterceptorEntry.Postion.LAST) {
                    b.addFirst(entry.interceptor);
                }
            }
        }
        if (responseInterceptors != null) {
            for (final ResponseInterceptorEntry entry: responseInterceptors) {
                if (entry.postion == ResponseInterceptorEntry.Postion.LAST) {
                    b.addFirst(entry.interceptor);
                }
            }
        }

        final HttpProcessor httpProcessor = b.build();
        execChainDefinition.addFirst(
                new AsyncProtocolExec(httpProcessor, targetAuthStrategyCopy, proxyAuthStrategyCopy),
                ChainElements.PROTOCOL.name());

        // Add request retry executor, if not disabled
        if (!automaticRetriesDisabled) {
            HttpRequestRetryHandler retryHandlerCopy = this.retryHandler;
            if (retryHandlerCopy == null) {
                retryHandlerCopy = DefaultHttpRequestRetryHandler.INSTANCE;
            }
            execChainDefinition.addFirst(
                    new AsyncRetryExec(retryHandlerCopy),
                    ChainElements.RETRY_IO_ERROR.name());
        }

        HttpRoutePlanner routePlannerCopy = this.routePlanner;
        if (routePlannerCopy == null) {
            SchemePortResolver schemePortResolverCopy = this.schemePortResolver;
            if (schemePortResolverCopy == null) {
                schemePortResolverCopy = DefaultSchemePortResolver.INSTANCE;
            }
            if (proxy != null) {
                routePlannerCopy = new DefaultProxyRoutePlanner(proxy, schemePortResolverCopy);
            } else if (systemProperties) {
                routePlannerCopy = new SystemDefaultRoutePlanner(
                        schemePortResolverCopy, ProxySelector.getDefault());
            } else {
                routePlannerCopy = new DefaultRoutePlanner(schemePortResolverCopy);
            }
        }

        // Add redirect executor, if not disabled
        if (!redirectHandlingDisabled) {
            RedirectStrategy redirectStrategyCopy = this.redirectStrategy;
            if (redirectStrategyCopy == null) {
                redirectStrategyCopy = DefaultRedirectStrategy.INSTANCE;
            }
            execChainDefinition.addFirst(
                    new AsyncRedirectExec(routePlannerCopy, redirectStrategyCopy),
                    ChainElements.REDIRECT.name());
        }

        List<Closeable> closeablesCopy = closeables != null ? new ArrayList<>(closeables) : null;
        if (!this.connManagerShared) {
            if (closeablesCopy == null) {
                closeablesCopy = new ArrayList<>(1);
            }
            if (evictExpiredConnections || evictIdleConnections) {
                if (connManagerCopy instanceof ConnPoolControl) {
                    final IdleConnectionEvictor connectionEvictor = new IdleConnectionEvictor((ConnPoolControl<?>) connManagerCopy,
                            maxIdleTime,  maxIdleTime);
                    closeablesCopy.add(new Closeable() {

                        @Override
                        public void close() throws IOException {
                            connectionEvictor.shutdown();
                        }

                    });
                    connectionEvictor.start();
                }
            }
            closeablesCopy.add(connManagerCopy);
        }
        ConnectionReuseStrategy reuseStrategyCopy = this.reuseStrategy;
        if (reuseStrategyCopy == null) {
            if (systemProperties) {
                final String s = System.getProperty("http.keepAlive", "true");
                if ("true".equalsIgnoreCase(s)) {
                    reuseStrategyCopy = DefaultConnectionReuseStrategy.INSTANCE;
                } else {
                    reuseStrategyCopy = new ConnectionReuseStrategy() {
                        @Override
                        public boolean keepAlive(
                                final HttpRequest request, final HttpResponse response, final HttpContext context) {
                            return false;
                        }
                    };
                }
            } else {
                reuseStrategyCopy = DefaultConnectionReuseStrategy.INSTANCE;
            }
        }
        final AsyncPushConsumerRegistry pushConsumerRegistry = new AsyncPushConsumerRegistry();
        final IOEventHandlerFactory ioEventHandlerFactory = new HttpAsyncClientEventHandlerFactory(
                new DefaultHttpProcessor(new H2RequestContent(), new H2RequestTargetHost(), new H2RequestConnControl()),
                new HandlerFactory<AsyncPushConsumer>() {

                    @Override
                    public AsyncPushConsumer create(final HttpRequest request) throws HttpException {
                        return pushConsumerRegistry.get(request);
                    }

                },
                versionPolicy != null ? versionPolicy : HttpVersionPolicy.NEGOTIATE,
                h2Config != null ? h2Config : H2Config.DEFAULT,
                h1Config != null ? h1Config : H1Config.DEFAULT,
                charCodingConfig != null ? charCodingConfig : CharCodingConfig.DEFAULT,
                reuseStrategyCopy);
        final DefaultConnectingIOReactor ioReactor;
        try {
            ioReactor = new DefaultConnectingIOReactor(
                    ioEventHandlerFactory,
                    ioReactorConfig != null ? ioReactorConfig : IOReactorConfig.DEFAULT,
                    threadFactory != null ? threadFactory : new DefaultThreadFactory("httpclient-dispatch", true),
                    new Callback<IOSession>() {

                        @Override
                        public void execute(final IOSession ioSession) {
                            ioSession.addFirst(new ShutdownCommand(ShutdownType.GRACEFUL));
                        }

                    });
        } catch (final IOReactorException ex) {
            throw new IllegalStateException(ex.getMessage(), ex);
        }

        if (execInterceptors != null) {
            for (final ExecInterceptorEntry entry: execInterceptors) {
                switch (entry.postion) {
                    case AFTER:
                        execChainDefinition.addAfter(entry.existing, entry.interceptor, entry.name);
                        break;
                    case BEFORE:
                        execChainDefinition.addBefore(entry.existing, entry.interceptor, entry.name);
                        break;
                }
            }
        }

        customizeExecChain(execChainDefinition);

        NamedElementChain<AsyncExecChainHandler>.Node current = execChainDefinition.getLast();
        AsyncExecChainElement execChain = null;
        while (current != null) {
            execChain = new AsyncExecChainElement(current.getValue(), execChain);
            current = current.getPrevious();
        }

        Lookup<AuthSchemeProvider> authSchemeRegistryCopy = this.authSchemeRegistry;
        if (authSchemeRegistryCopy == null) {
            authSchemeRegistryCopy = RegistryBuilder.<AuthSchemeProvider>create()
                    .register(AuthSchemes.BASIC, new BasicSchemeFactory())
                    .register(AuthSchemes.DIGEST, new DigestSchemeFactory())
                    .register(AuthSchemes.CREDSSP, new CredSspSchemeFactory())
                    .register(AuthSchemes.NTLM, new NTLMSchemeFactory())
                    .register(AuthSchemes.SPNEGO, new SPNegoSchemeFactory(SystemDefaultDnsResolver.INSTANCE, true, true))
                    .register(AuthSchemes.KERBEROS, new KerberosSchemeFactory(SystemDefaultDnsResolver.INSTANCE, true, true))
                    .build();
        }
        Lookup<CookieSpecProvider> cookieSpecRegistryCopy = this.cookieSpecRegistry;
        if (cookieSpecRegistryCopy == null) {
            cookieSpecRegistryCopy = CookieSpecRegistries.createDefault();
        }

        CookieStore cookieStoreCopy = this.cookieStore;
        if (cookieStoreCopy == null) {
            cookieStoreCopy = new BasicCookieStore();
        }

        CredentialsProvider credentialsProviderCopy = this.credentialsProvider;
        if (credentialsProviderCopy == null) {
            if (systemProperties) {
                credentialsProviderCopy = new SystemDefaultCredentialsProvider();
            } else {
                credentialsProviderCopy = new BasicCredentialsProvider();
            }
        }

        return new InternalHttpAsyncClient(
                ioReactor,
                execChain,
                pushConsumerRegistry,
                threadFactory != null ? threadFactory : new DefaultThreadFactory("httpclient-main", true),
                connManagerCopy,
                routePlannerCopy,
                versionPolicy != null ? versionPolicy : HttpVersionPolicy.NEGOTIATE,
                cookieSpecRegistryCopy,
                authSchemeRegistryCopy,
                cookieStoreCopy,
                credentialsProviderCopy,
                defaultRequestConfig,
                closeablesCopy);
    }

}